1. Field of the Invention
The present invention relates to a spindle motor for a disk drive and in particular to a spindle motor capable of damping and isolating mechanical vibration and noise generated in the spindle motor stator and bearings.
2. Description of the Related Art
There is currently a large demand for disk drives for use in servers, desktop computers and laptops. Disk drive manufacturers are meeting this demand with drives having improved drive performance and higher storage capacities in the same size or smaller form factor. In general, a disk drive includes a head disk assembly (HDA) and control electronics. The HDA consists of an enclosure housing a head stack assembly and one or more magnetic storage disks rotated by a spindle motor. The head stack assembly includes a pivot bearing assembly for pivotally supporting a rotary actuator having one or more read/write heads. As the storage disk is rotated, the read/write head is pivoted across a surface of the storage disk on an air bearing so that information may be transferred to and from the disk under the direction of the control electronics.
One important drive performance characteristic is the level of mechanical vibration emanating from the drive. Large mechanical vibration can adversely affect drive performance. A corollary effect of mechanical vibration is acoustic noise. Acoustic noise emanating from a drive can create the appearance of poor quality. Additionally, standards for acceptable acoustic noise levels, set by the International Standards Organization (ISO), are becoming more stringent as computers become further integrated into the workplace and home.
A significant source of mechanical vibration within a disk drive is the spindle motor. A disk drive spindle motor typically includes a base and a central shaft for securing the spindle motor to the disk drive enclosure. A hub for supporting the storage disks is rotationally mounted to the shaft by a pair of bearings. The spindle motor further includes a rotor fixedly mounted to the hub and a stator fixedly mounted to the shaft, which together generate torque for rotating the hub. In particular, the stator includes a series of electrically conductive coils wrapped around cores which are arranged radially around the shaft. Leading portions of the stator wires extend downwardly from the core and are electrically connected to the drive control electronics. The various coils of the stator are selectively energized, via signals from the printed circuit board assembly, to form an electromagnet that pulls/pushes on a permanent magnet forming part of the rotor. The magnetic interaction between the stator and rotor imparts a rotational motion to the rotor, hub and storage disk(s) attached to the hub.
For brushless spindle motors, the electric current supplied to the coils of the stator is rapidly switched to maintain the stator magnetic field such that the rotor and hub continue to rotate. This switching frequency generates mechanical vibration and noise. The vibration and noise are also compounded by tolerances within the bearings on which the hub and rotor are rotationally supported. This vibration and noise are transmitted through the spindle motor base and shaft to the drive enclosure, which can amplify the vibration and noise, particularly at resonant frequency, due to its large surface area. Moreover, the problem of vibration and noise becomes worse at higher rotational speeds. As drive manufacturers are constantly striving for higher rotational speeds to increase data transfer-rates, the vibratory response of the spindle motor is of critical importance to disk drive manufacturers.
Embodiments of the present invention relate to a spindle motor for a disk drive, the spindle motor including a mounting structure having a bracket and/or a shaft that mount to the disk drive base and cover, respectively. The motor further includes a carrier assembly including a carrier mounted to the mounting structure. The carrier in turn supports the spindle motor hub, bearings, rotor and stator.
In order to prevent mechanical vibration and noise generated within the motor from being transmitted to the drive enclosure, the carrier assembly is mounted on the mounting structure by an elastomeric damper. In one embodiment, the elastomeric damper may comprise a pair of O-rings interposed at an interface between the mounting structure and the carrier so that no direct contact between the mounting structure and the carrier assembly occurs. As a result, mechanical noise and vibration from the carrier assembly is isolated and not transmitted to the mounting structure or drive enclosure.
In one embodiment, each O-ring lies snugly within an interface between a pair of generally perpendicular surfaces of the mounting structure and a surface of the carrier that is inclined at an oblique angle with respect to the mounting structure surfaces. With such an orientation, the O-rings are able to support the carrier to prevent horizontal and vertical movement of the carrier assembly relative to the mounting structure, and are able to isolate and dampen both horizontal and vertical components of mechanical vibration from the carrier assembly.